Printed-wiring technology is currently used to fabricate circuit boards having embedded circuit traces. These traces are interconnected by “vias,” or plated thru-holes, that connect one trace on one circuit board layer to another trace on a different layer. In electronic systems, there are a variety of electrical connection types between the circuit board and the components such as integrated circuits that are attached to the circuit board. As integrated circuits become more dense, so too must the electrical connections.
A land grid array (LGA) is an electrical connection interface for components, such as microprocessors. Unlike the pin grid array (PGA) interface commonly found on integrated circuits, with LGA, there are no pins on the chip; in place of the pins are pads of bare gold-plated copper that touch pins on the circuit board. Such LGAs offer high interconnection density (e.g., at a one millimeter pitch, a 35×35 grid may contain 1,225 interconnections in a space less than 1.5 square inches and 2,025 interconnections in a 45×45 grid less than 1.75 square inches). LGAs are easy to manufacture and the cost of module production is much less because terminations such as pins or balls are no longer required.
Many modern circuit boards for use with LGAs or other electrical connection interfaces have a very large number of connections and vias extending from the external connections on one surface of the circuit board to internal wiring, and to wiring and connections on the opposite surface of the circuit board. In many instances, if a few or even one of these connections is defective, the entire board is defective and the connection and associated via must either be repaired or replaced, or the entire board has to be scrapped.
One known solution for working with damaged LGA pads is to remove the damaged pad and utilize a lily pad-shaped repair pad that is etched on a printed circuit board, as shown in FIG. 1. The pad 102 has a tail section 104 that is able to be inserted through a via of a multilayer circuit board and soldered on the opposite side of the circuit board. Conventional lily pad-shaped repair pads are manufactured by etching the pad 102 onto a copper-plated board 124, and then cutting along lines 106-122 to remove the pad. Once the pad 102 is removed from the circuit board 124, the tail 104 is folded down so that it can be inserted into the appropriate via. Unfortunately, as shown in FIG. 2, this leaves a void 202 in the portion of the pad 102 that is to be used to make contact with a component. This results in a repaired site with a pad that does not have a round and smooth contact pad surface. This presents a problem, particularly with components that have spring movement contact arms.
Spring movement LGA socket devices, such as the Tyco “cantilevered-spring,” typically reduce co-planarity problems by effectively taking up slack when there is a problem with co-planarity on the bottom of the device. However, spring contacts move as the component is pressed against the LGA pads.
Because of the irregular surface of the lily pad-shaped pad, attachment mechanisms such as a cantilevered-type spring connector cannot be used, as the tip of the connector may bind on the gap 202 on the repaired pad 102 during the mating/compression process, causing further damage to the repaired pad or damage to the interconnect device.
Another known solution is to use a replacement pad and a wire that runs through the circuit board. More specifically, in this repair process the damaged pad is removed from one side of the circuit board. The wire is inserted into the via and ran through so as to protrude on the opposite side of the circuit board. The replacement pad is attached to the area from which the damaged pad was removed using an adhesive, and the wire is soldered to the replacement pad. The wire protruding oil the opposite side of the circuit board is soldered to the via and the excess wire is clipped so as to make it flush with the circuit board. While the damaged pad is replaced, this repair process requires the creation of a second solder connection on the underside of the repair pad, which creates another point of failure.